This invention relates to the resolution of alpha and beta pinene mixtures and particularly to the treatment of terpene fractions containing alpha and beta pinene.
Customarily, naturally-occurring beta pinene has been isolated from certain alpha pinene-rich turpentines, e.g. gum and sulfate turpentine. Beta-pinene is useful as a raw material for producing terpene resins and Nopol (6,6-dimethyl bicyclo (3,1,1)-2-heptene-2-ethanol) regardless of its optical configuration, and is particularly valuable as a raw material in the synthesis of fine chemicals such as 1-menthol and dl-citronellol when such pinene has high optical activity (laevo rotation).
Alpha pinene is much more abundant and has been less valuable as a starting material for chemical synthesis, when compared with beta pinene. Mixtures of alpha pinene and beta pinene rich in beta pinene are obtainable by means well known in the art, for example according to the process taught in U.S. Pat. No. 3,278,623 issued on Oct. 11, 1966 which process comprises establishing contact between a supply of a mixture of alpha-pinene and beta-pinene and a transitory hydrogen acceptor catalyst which is one or more of the elements of Group VIII having an atomic number between 28 and 78 or palladium chloride or platinum oxide under neutral to basic conditions in a reaction zone maintained between room temperature and about 300.degree. C. and withdrawing from the reaction zone mixtures richer in beta pinene.
One of the most efficient methods of recovering an ingredient from a mixture of liquid, or liquifiable ingredients is by fractional distillation. Yet so far as is known it has not heretofore been possible to recover beta pinene by distillation in a substantially pure state from mixtures of alpha pinene and beta pinene. This past inability to recover beta pinene in a highly purified state and at low cost by distillation is due to the fact that the volatility of alpha pinene relative to beta pinene is low.
Azeotropes of alpha pinene with another chemical compound are known, (e.g. ethylene glycol) as are azeotropes of beta pinene with other chemical compounds known. See Lecat, "Tables Azeotropiques"/Tome Premier 2nd Ed/UCCLE-Bruxelles, July, 1949, Page 147. However, no azeotropes are indicated in the prior art to exist having the following properties with respect to alpha pinene and beta pinene:
1. An azeotroping chemical having a relatively low cost yet having a relatively high stability and low solubility in each of alpha pinene and beta pinene;
2. An azeotroping chemical having a boiling point (at a given pressure) greater than either of the boiling points of alpha pinene or the boiling point of beta pinene;
3. An azeotroping chemical having such physical properties whereby only small amounts of azeotrope co-distill with the beta pinene (that is, the composition of distillate product contains at most 15 mole % azeotroping agent).
4. An azeotroping chemical which allows a reduction of the number of distillation column plates or stages which are required to effect the separation required, or alternatively, and preferably, allows a reduction in the amount of reflux required in a column having the same number of plates or stages whereby a reduction in the quantity of energy required to cool the condenser and impart heat to the reboiler is effected; and
5. An azeotroping agent, the use of which in a batch distillation will permit a substantial increase in throughput (grams/hour of beta-pinene product) for the same strength of resulting beta-pinene product; and gives rise to a substantially diminished time of distillation and a lesser total quantity of energy input to the system
The use of diethylene glycol as an entrainer useful in facilitating the separation of pairs of compounds is known generally in the art; but not specifically with respect to terpene compound mixture separation.
Thus U.S. Pat. No. 2,265,939 issued on Dec. 9, 1941 discloses a method of separating phenol from its mixture with cyclohexanone by adding to the mixture one of a group of compounds, including diethylene glycol, and separating phenol from the resultant mixture by distillation.
In addition, in accordance with U.S. Pat. No. 3,125,496 issued on Mar. 17, 1964 .alpha.-naphthol is stated to be recovered in a highly purified state from mixtures thereof with tetralol and tetralone by subjecting such mixtures to fractional distillation in the presence of diethylene glycol which forms an azeotropic mixture with tetralone but does not form an azeotropic mixture with .alpha.-naphthol.
U.S. Pat. No. 3,655,803 (Class 260, subclass 675.5) issued on Apr. 11, 1972, discloses a technique for producing an .alpha.-pinene product of low sulfur content by continuously fractionally distilling crude sulfate turpentine into a sulfur rich overhead distillate fraction having an .alpha.-pinene content between 2 and 20 weight percent, and a bottoms fraction of higher boiling materials, and fractionally distilling the bottoms fraction to recover product as an .alpha.-pinene distillate fraction.